Endoluminal devices comprise the general category of devices, such as stents, grafts, combinations thereof commonly referred to as stent-grafts or endoluminal prostheses, vena cava filters, and the like, that may be implanted in a body lumen. Endoluminal devices may be implanted by so-called “minimally invasive techniques” in which the prosthesis, restrained in a radially compressed configuration by a sheath or catheter, is delivered by a deployment system or “introducer” to the site where it is required. The introducer may enter the body through the patient's skin, or by a “cut down” technique in which the entry lumen, such as a blood vessel, is exposed by minor surgical means. When the introducer has been threaded into the body lumen to the prosthesis deployment location, the introducer is manipulated to cause the endoluminal device to be ejected from the surrounding sheath or catheter in which it is restrained (or alternatively the surrounding sheath or catheter is retracted from the endoluminal device), whereupon the endoluminal device expands to a predetermined diameter at the deployment location, and the introducer is withdrawn.
As referred to herein, “distal” refers to the direction further away from the insertion point and “proximal” refers to the direction closer to the insertion point. Endoluminal devices, such as stents and vena cava filters, may expand by spring elasticity, balloon expansion, or by the self-expansion of a thermally or stress-induced return of a memory material to a pre-conditioned expanded configuration.
Various types of endoluminal device architectures, are known in the art, including many designs comprising a filament or number of filaments, such as a wire or wires, wound or braided into a particular configuration. Included among these configurations are braided stents, such as is described in U.S. Pat. No. 4,655,771 to Hans I. Wallsten and incorporated herein by reference; the '771 Wallsten patent is only one example of many variations of braided architecture known in the art and thus is not intended as a limitation of the invention described herein later. Braided endoluminal devices tend to be very flexible, having the ability to be placed in tortuous anatomy and still maintain patency. The flexibility of braided stents make them particularly well-suited for treating aneurysms in the aorta, where often the lumen of the vessel becomes contorted and irregular both before and after placement of the stent.
Many braided endoluminal devices experience “foreshortening” when deployed in a body lumen. Referring now to FIGS. 1A–1C, showing an exemplary delivery system 20 of the prior art, stent 10 may have a first length LC when radially compressed as shown in FIG. 1A and a second, shorter length LE when radially expanded, as shown in FIG. 1C. The “foreshortening ratio”
            L      C        -          L      E            L    E  can be used as a measure of the relative change in length. Braided endoluminal devices typically have a relatively large foreshortening ratio as compared to non-braided endoluminal devices. The foreshortening ratio is a function of compressed diameter, deployed diameter, and the braid angle. If these variables are known, the endoluminal device has a predictable foreshortening ratio.
Foreshortening may affect the deployment accuracy of endoluminal devices. Describing delivery system 20 now in more detail, the delivery system comprises a handle 22, a tip 24, an inner member 26 attached to the tip and the handle, a pusher 27 positioned proximally of stent 10, and an outer sheath 28 slidable relative to the inner member and pusher. Inner member 26 may have one or more protrusions 25 thereon for engaging the stent during deployment, such as are disclosed in U.S. Pat. No. 6,607,551 to Sullivan et al., incorporated herein by reference. Stent 10 may be a braided stent having a wound end 11, such as is described in U.S. Pat. No. 6,585,758 to Chouinard et al. and incorporated herein by reference. Delivery system 20 is maneuvered into the body lumen (not shown) so that the distal end 12 of stent 10 is aligned with a desired deployment location 29 in the lumen, as shown in FIG. 1A. FIGS. 1A–1C are shown in vertical alignment with one another on the page so that desired deployment location 29 is in the same horizontal position in all figures for illustrative purposes.
To deploy the stent, outer sheath 28 is retracted in the direction of arrow A as shown in FIG. 1B. As stent 10 begins to deploy, it also foreshortens, causing distal end 12 of stent 10 to be move proximally from the desired deployment location 29. Thus, after full deployment as shown in FIG. 1C, continued foreshortening during deployment may cause the ultimate resting position of distal end 12 to be a distance dL from the desired deployment location 29. This distance dL is typically approximately the difference in length between the radially compressed length LC and the expanded length LE. In some cases, distal end 12 of stent 10 may frictionally engage a portion of the body lumen in which the stent is being deployed before the stent is completely deployed. In such cases, a portion of the length accounting for the difference between the compressed length LC and the expanded length LE of the stent will be proximal to the deployed stent. Thus, even though this distance may be predictable, practitioners must determine the correct place to start deployment based upon where the end of the stent is expected to land after foreshortening. Deploying such stents with accuracy, therefore, takes repeated practice and is prone to error.
It is therefore desirable to minimize the impact of foreshortening of braided endoluminal devices during deployment so that such endoluminal devices can be more accurately deployed.